to widen the bridge walkway. Another stair rose from the northern BMT mezzanine to the northwestern corner of Centre Street and Duane Street (east of the current Foley Square entrance), though this was also sealed by 1992 to reduce the maintenance costs associated with maintaining two adjacent staircases. The northern BMT mezzanine contained bronze doors on the east wall, now sealed, which led to the Thurgood Marshall United States Courthouse. Under the northern side of the Manhattan Municipal Building were additional subway staircases, although this entrance area was closed by 1938. BMT Nassau Street Line platforms The Chambers Street station on the BMT Nassau Street Line is beneath the Manhattan Municipal Building, stretching from Duane Street in the north to a point just south of Chambers Street to the south. The J stops here at all times and the Z stops here during rush hours in the peak direction. The Chambers Street station has four tracks, three island platforms, and one side platform (originally two); the westernmost side platform has been demolished, while the center island platform and the easternmost side platform are unused. From the BMT station, there are stairs and elevators leading to the mezzanines above. The easternmost side platform had seven stairs, while the center island platform and the westernmost side platform had six stairs. The eastern island platform has five stairs and the western island platform has four stairs. The elevators are at the southern ends of the western and eastern island platforms. The island platforms allow for cross-platform interchanges between local and express trains heading in the same direction. Terminating trains use the inner tracks while through trains use the outer tracks. The platforms are long, and the station is approximately wide. The southbound platform is slightly higher at the southern end of the station because the next stop south, Fulton Street, is bi-level with the southbound platform being above the northern one. Design Like the IRT station, the tunnel is covered by a "U"-shaped trough that contains utility pipes and wires. The bottom of this trough contains a foundation of concrete no less than thick. Each platform consists of concrete slabs, beneath which are drainage basins. The platforms contain double-height, tile-clad columns spaced every , which support the jack-arched concrete station roofs. There is a gap between the trough wall and the platform walls, which are made of -thick brick covered over by a